Research on confining pressure effect of pore structure of coal-rich in coalbed methane under cyclic impact

Abstract

Coal seam penetration modification is the primary technical problem facing the efficient development of coalbed methane and coal mine methane control. To study the effect of cyclic impact load on the permeability of coal rock under the confining pressure, the dynamic mechanical properties and the pore evolution of coal were conducted by using the separated Hopkinson pressure bar (SHPB) and the low-field nuclear magnetic resonance (NMR) technique. The results showed that the dynamic compressive strength existed as a turning point at a critical confining pressure of 6 MPa and the spectrum area growth rate of adsorption pores was negatively correlated with that of seepage pores. As the confining pressure increased, the pattern of the effective porosity growth rate of the coal was positively correlated with the peak compressive strength, meanwhile, the permeability growth rate of the coal showed an exponential growth trend. The evolution pattern of the permeability under the coupled action of the confining pressure and impact pressure was obtained. In addition, based on the U-shaped distribution of permeability growth rate and effective porosity growth rate with the impact pressure, an exponential relationship between them was derived. The related research results could provide important theoretical support for coalbed methane exploitation.